(a) Field of the Invention
The present invention relates to a monofilament having a segmented pie structure formed by conjugated spinning of degradable polymers and non-degradable polymers, a hernia mesh comprising the monofilament having improved flexibility and biocompatibility, and a method for preparing the same. More specifically, the present invention relates to a monofilament prepared by conjugated spinning of degradable polymers and non-degradable polymers in the form of a segmented pie; a hernia mesh that is prepared with the monofilament and that is controlled to be gradually degraded in the body while losing the stiffness of the early stage, causing no misfeelings, and having improved flexibility and biocompatibility; and a method of preparation thereof.
(b) Description of the Related Art
Tension-free hernioplasty (Lichtenstein I L, Am J Surg 1989; 157; 188-193) is considered to be a useful method for reparation of hernias, because the relapse ratio thereafter is low, the operative time is short, and the operative wound heals quickly, and thereby the patient can rapidly return to normal life. Conventionally, since the mesh used for hernia repair is required to have the capability of maintaining its chemical and physical properties for several years to strengthen the peritoneum, polypropylene monofilaments have been used as the material for a hernia mesh. However, it has been reported that the polypropylene mesh may have the potential to generate fistulas in the intestine (Seelig M H, “A rare complication after incisional hernia repair”. Chirurg 1995; 66(7); 739-741, Leber G E, “Long-term complications associated with prosthetic repair of incisional hernias”, Arch Surg 1988; 133(4); 378-382). Further, as general side effects of the polypropylene mesh, an edema, a restriction of abdominal wall mobility due to stiffness of the peritoneum where the artificial membrane is located and pain from misfeelings caused by the stiffness, a chronic inflammatory response between the polypropylene fibers and tissues in body, and the like have been reported (Amid P K, “Biomaterials for abdominal wall hernia surgery and principles of their applications”, Lagenbecks Arch Chir 1994; 379(3): 168-171, Waldrep D J, “Mature fibrous cyst formation after Marlex Vestweber K, Results of recurrent abdominal wall hernia repair using polypropylene mesh”. Zentralblatt Für Chirurgie 1997; 122:885-8, Belton J M, “Integration of biomaterials implanted into abdominal wall: mesh ventral herniorrhaphy: a newly described pathologic entity”. Am Surg 1993; 59(11):716-8, “Process of scar formation and macrophage response”. Biomaterials 1995; 16(5):381-7, Klinge U, “Changes in abdominal wall mechanics after mesh implantation”. Experimental changes in mesh stability. Lagenbecks Arch Chir 1996; 381(6): 323-32).
The hernia mesh needs stiffness in order to be positioned and fixed on the surgical wound region when performing the surgical operation. For that purpose, several methods to prepare the hernia mesh using fibers in the monofilament form have been known. U.S. Pat. No. 4,347,847, U.S. Pat. No. 4,452,245, U.S. Pat. No. 5,569,273, and U.S. Pat. No. 6,287,316 disclose a method to prepare a hernia mesh consisting of polypropylene monofilaments. However, since polypropylene is non-degradable, after performing the surgical operation using the hernia mesh, the strength and stiffness of the mesh that are necessary during the initial stage after the surgical operation are continuously maintained in the body. Therefore, the mesh has excessive stiffness even after the wound has healed, causing pain to the patient due to misfeelings. Further, U.S. Pat. No. 5,292,328 discloses a method of preparing a hernia mesh consisting of polypropylene multifilaments in order to improve the flexibility, in which the mesh has a somewhat improved initial flexibility compared with that consisting of the monofilaments. However, since the mesh consists of only non-degradable materials, there are also some problems in that the initial strength and stiffness of the mesh are continuously maintained in the body, and an excessive amount of polypropylene remains in the body.
To solve these problems, studies on development of a partially degradable mesh wherein the content of polypropylene is decreased and the strength and stiffness necessary for the initial stage is supplemented by additionally comprising degradable materials, have been disclosed in U.S. Pat. No. 4,652,264 and U.S. Pat. No. 6,162,962. Herein, the degradable materials are partially degraded after the wound has healed, to improve the flexibility of the mesh. U.S. Pat. No. 4,652,264 discloses a method to prepare a mesh by combining threads consisting of three different materials, of which two are degradable and one is non-degradable. U.S. Pat. No. 6,287,316 discloses a method of preparing a mesh using a multifilament consisting of degradable materials and non-degradable materials. However, since the meshes prepared by the above methods consist of several threads of degradable and non-degradable materials in the combined form, there is a possibility of bacterial infection within the spaces between the threads, which is an inherent defect of multifilaments. Further, since the methods employ the multifilament form wherein several strands of fiber are combined, the amount of materials required for exhibiting the necessary stiffness is larger than the case of using the monofilament. In addition, the multifilament causes a strong foreign body response due to the large surface area (Beets G L, “Foreign body reactions to monofilament and braided polypropylene mesh used as preperitoneal implants in pigs”. Eur J Surg 1996; 162:823-825).
As known from the above prior art, although the use of a hernia mesh has been regarded as a basic means in performing hernia repairs, there are unsatisfactory results obtained from the studies to develop a hernia mesh for improving the convenience in performing the operation, reducing the misfeelings, and having improved biocompatibility. Therefore, it is required to develop a hernia mesh that can maintain its strength and stiffness at the early stage, thereby ensuring convenience in performing the operation, and be partially degraded as the surgical wound is healed, thereby improving the flexibility of the remaining mesh.